Question: Regarding mechanics of Opcode #1 Stat: Attacks Per Round Modifier

So I’m planning on making a mod where each class gains base APR as they level, similar to the default fighter, albeit at different rates; and moreover make weapon proficiency APR gain universal in the standard method by editing the WSPATCK.2da and the CLSWPBON.2DA files. Now, as such, all class APR should be granted with innate effects granted per certain levels using Opcode 1 (Stat: Attacks Per Round Modifier) via the CLAB tables. Now I should like to make sure that these Opcodes do not stack in the case of Multi/Dual classes (where the two classes would each have their own APR bonuses). I am correct in assuming that the Opcode’s type value should be set to 1 (Flat Value Modifier) rather than 0 (Cumulative Modifier)? Thus the opcodes will set the base APR and not stack, that is, as far as I’ve tested, the APR Opcode with the highest APR value will override the others, rather than, as with a cumulative type, all add together?

This is my hypothetical understanding of how the Flat Value Modifier would work:
There is a Fighter / Cleric whose Fighter level makes their Base APR 2 (essentially a + 1 bonus) and whose Cleric level makes their Base APR 1.5 (essentially a +0.5 bonus). Using the Flat Value Modifier this Fighter/Cleric’s base APR with be 2, whereas if I used the Cumulative Modifier it would be 2.5.

Is my understanding correct? Moreover is there any potential problems (anyone can foresee) using this method for APR progression will cause with any of the already existing mechanics of the game? Like, for example Whirlwind Attack?